The invention relates to a flat lighting device.
In particular, what is involved is a lighting device for lighting spaces, for example in buildings or mobile facilities such as, for example, vehicles or aircraft and ships. Various aspects are to be considered in this case such as, for example, the desired light intensity distribution in the space, the color temperature of the light, but also architectural and economic aspects. Moreover, for physiological and economic reasons daylight is also usually included in the light planning of rooms in buildings.
Daylight obtained with the aid of windows is generally used to light rooms of buildings. Given good daylight conditions, artificial light sources can be dispensed with in some circumstances by careful selection of the size and number of the windows. Artificial light sources are indispensable for interior lighting, at least given unfavorable daylight conditions and in the case of darkness. This problem has been resolved to date by providing within the room xe2x80x94in addition to the window or windows for utilizing the daylightxe2x80x94further light sources, for example electric lamps, candles, optical conductors etc. It is disadvantageous, inter alia, that the light intensity distribution inside the room changes with the change in illumination from daylight to artificial light.
It is the object of the present invention to circumvent the disadvantage of the prior art and provide a lighting device which is improved for this purpose.
This object is achieved with a flat lighting device having the features of claim 1. Particularly advantageous refinements are to be found in the dependent claims.
The basic idea of the invention consists in integrating the daylight and the artificial light for interior lighting in a single flat lighting device. Put simply, the realization of this basic idea can be seen in suitably modifying a flat lamp in such a way that the latter can also be used as a window, or else, regarded in the opposite way, in suitably modifying a window in such a way that the latter also functions as a lamp.
The lighting device according to the invention is not limited in this case to the possible use of daylight in the strict sense, that is to say to the configuration in the form of an xe2x80x9couter windowxe2x80x9d lighting device, but rather the latter is merely to be highlighted here as a particularly interesting variant. Rather, interest also attaches to the additional use of other light sources for backlighting the lighting device, for example in the form of an xe2x80x9cinner windowxe2x80x9d lighting device of a room divider, as a result of which it is also possible, if appropriate, to use the light of the adjoining room.
All that is essential for the purpose of the invention is for the lighting device both to have transparent regions for the light from the backlighting source, for example daylight, ambient light, through which, if appropriate, the daylight or, more generally, background light can pass and to have regions which shine owing to one or more integrated artificial light sources inside the lighting device.
For this purpose, the flat lighting device according to the invention has two extended view surfaces, which are situated opposite one another and are at least partially transparent, and at least one integrated light source, for example a flat fluorescent lamp. The, or each, electric light source is designed and arranged in such a way that the latter defines a corresponding luminous area inside at least one of the two view surfaces. A transparent part of the view surface adjoins the, or each, luminous area in each case. The term xe2x80x9ctransparentxe2x80x9d which has been used is intended to be understood as generalizing the invention to the extent that both transparent, that is to say clear, and only translucent, for example matt or dull materials are covered for said regions. All that is essential is for at least a portion of the light of the backlighting (daylight, ambient light, or the like) to be passed through these regions.
It can, in particular, also be advantageous to construct at least one luminous area in each case inside both view surfaces. In this case, the lighting device specifically shines to both sides when operating. It is therefore possible, for example, in the case of application to an outer window, to implement interior lighting on the view surface of the lighting device facing the interior, and a luminous advertisement, an information sign or some other luminous information content on the view surface facing outward.
It is advisable to tune the ratio between the total luminous area and the entire transparent or translucent part of the respective view surface for the purpose of a compromise which is suitable in practical terms between the function as a window on the one hand, and the function as a lamp during operation, on the other hand. However, there is no need for this compromise if success is achieved in likewise designing the, or each, integrated light source of the lighting device according to the invention to be at least partially transparent. The point is that the regions of the light source which act as a luminous area during operation then likewise act in the disconnected state as transparent or translucent parts of the two view surfaces, that is to say, if appropriate, the total view surface of the flat lighting device then acts as a window. This aspect is taken up again further below.
It is advantageous in each case to select the number, dimensions and distribution of the integrated light sources, and consequently of the luminous areas, for the purpose of being able to generate in operation a spatial light distribution similar to daylight.
Strip-shaped light sources alternating with likewise strip-shaped transparent or translucent regions have proved, inter alia, to be suitable in this context. Otherwise, however, the most varied shapes are also suitable. The presentation is subject to certain limits in this regard, however, owing to esthetic viewpoints and considerations of the possibility of economic production. Suitable, inter alia, in any event are light sources with shapes which are circular or at least resemble a circle, for example oval or elliptical as well as rectangular, diamond-shaped, hexagonal or similarly shaped ones which are arranged distributed within the two surfaces and are adjoined by transparent regions. Reference is made to the exemplary embodiments for further details on this.
By way of example, a suitably shaped flat, closed electric lamp, for example a flat gas discharge lamp, is suitable for the, or each, integrated light source.
In a preferred design, the, or each, electric lamp is designed as a flat gas discharge lamp with dielectrically impeded electrodes. Specifically, this type of lamp has an at least partially transparent flat discharge vessel which is filled with an ionizable filling, for example xenon, and has a baseplate and a front plate which typically consist of an at least substantially transparent insulant, for example glass. Dielectrically impeded electrode tracks are arranged on the baseplate and/or front plate in such a way that the front plate acts as a luminous area during operation.
According to the invention, the individual flat lamps are arranged on the glass plate of a window or else between the two glass plates of a double window. In any event, during operation the front plate (luminous on one side) and optionally also the baseplate (luminous on both sides) of each flat lamp likewise correspond(s) to a luminous area. Reference may be made to the publication WO-98/43277, whose disclosure is hereby taken as reference, for further details relating to the design of such flat lamps. In the case of the double window, the regions of the glass plate of the window, or the two glass plates, adjoining the two-dimensional extent of the front plate or baseplate of each flat lamp function as transparent regions within the two view surfaces of the arrangement. This ensures that the light from backlighting, for example daylight, can pass through these regions and contribute in this way to the overall luminous efficacy of the lighting device.
The advantage of this approach is, inter alia, the modular design which can be scaled in principle for windows of virtually any dimensions. Furthermore, the need for expensive filling gases, xenon in the example, is limited to the inner volumes of the relatively compact discharge vessels of the individual lamp modules.
A further preferred variant relates to a modified double window, in which the two glass plates act simultaneously as baseplate and front plate, respectively, of a single flat lamp. The dimensions of the flat lamp thus correspond substantially to those of the glass plates of the modified double window. The front and rear view surfaces of the lighting device are therefore formed by the outer wall of the front plate and baseplate, respectively. The two glass plates are connected in a gastight fashion to a discharge vessel, for example with the aid of a circumferential frame between the two plates. The individual light sources are implemented by arranging groups of electrode tracks on the baseplate and/or front plate, for example by means of conventional printing technology. The entire lamp is subdivided in this way, as it were, into a plurality of segments which act in each case as light sources. The shape of the, or each, luminous area corresponds substantially to that of the corresponding electrode group. The latter can be brought into virtually any desired flat shape in a simple way known per se, for example by means of printing processes known from thin-film and/or thick-film technology. The subregions surrounding the lamp segments act like a conventional window, that is to say they are transparent to daylight (or to background lighting in general). Ideally, the transparent regions consist of glass or another similarly transparent insulant in order to weaken as little as possible the background lighting passing through. However, the invention is to be regarded in a generalized fashion to the effect that even materials which are less effectively transparent, for example dully translucent materials, are also included.
The individual electrode groups can also, however, be capable of being driven separately, for example for a dimming operation, a flashing function or other visual lighting effects.
In any case, the, or each, region of the front plate which is provided as a luminous area during operation is provided with a fluorescent layer. In order to increase the luminance on the front plate, the, or each, region of the baseplate which is produced on the front plate by projecting a region, coated with fluorescent material, can have a light-reflecting layer.
The advantage of this variant is the relative ease with which it can be produced with relatively few production steps, since what is involved here is not, as previously, closed lamp modules which are to be produced individually, but just individual similar segments of a single lamp. The printing technology previously mentioned and capable of effective scaling in terms of area is, for example well suited to this purpose; in this case all the electrode groups of the overall window plate are applied by means of a single printing process. However, it is disadvantageous that because of the comparatively large volume of the double window discharge vessel, the quantity of filling gas, for example xenon, which is sometimes expensive, is likewise relatively large. Reference is made to the publication EP 0 926 705 A1, whose disclosure is hereby taken in reference, for further details with regard to flat lamps with dielectrically impeded electrode groups.
According to the present state of development, light yields of approximately 28 lm/W and light intensities per electric power (efficiency) of approximately 10 cd/W can be realized with such flat lamps on the basis of dielectrically impeded discharges. Depending on the target luminance of the luminous area and on the desired luminous flux emitted by the lighting device, it is possible to estimate therefrom the fraction of the luminous area required in relation to the entire view surface.
Table 1, which follows, is intended to illustrate this, the table being based, in addition to the abovementioned values for the light yield and efficiency, on a lighting device with a view surface of 1 m2 (corresponding to 100%) and a luminance of 5000 cd/m2 (that is to say largely non-glare and therefore suitable for interior lighting).
As shown by comparison with the luminous flux of a 100 W incandescent lamp of typically 1380 lm, there is a need in practice for luminous area fractions of more than 1%, typically at least a few percent, in order in any event to ensure an adequate level of lighting in interiors. On the other hand, the transparent part is generally not less than 1%, typically not less than a few percent, because otherwise the fraction of the light from the background lighting (daylight, ambient light, lighting of a neighboring room etc.) passing through is too low. An exception here is constituted by the variant in which the luminous areas, electrodes and other lamp components are themselves likewise (partially) transparent. It is possible in principle in this case for the entire view surface to be designed as a transparent luminous area. The dual function, mentioned at the beginning, of the lighting device is fulfilled even then.
Table 2, which follows, relates to a targeted luminance of approximately 7000 cd/m2 such as is suitable for exterior applications, for example for advertising purposes.